1. Field of the Invention
The present invention relates to a technique for detecting defects of a pattern formed on a substrate.
2. Description of the Background Art
In a field of inspecting a pattern formed on a semiconductor substrate, a glass substrate, a printed circuit board, or the like (hereinafter, referred to as “substrate”), conventionally, a comparison check method has been used. For example, from a grayscale target image to be inspected and a grayscale reference image, a differential absolute value image representing absolute values of differences in pixel value between these images is obtained and each of pixels in this image is binarized by a predetermined threshold value, to detect a region specified on a pixel basis as a defect.
Japanese Patent Application Laid Open Gazette No. 11-135583 (Document 1) discloses a method for detecting a defect with high accuracy with detection sensitivity in accordance with each inspection region, from a grayscale differential image generated with a grayscale conversion parameter and a threshold pixel value for each inspection region.
On a substrate, usually, a variety of patterns are formed. In a case where a very fine and dense wiring pattern is formed, for example, even a defect whose size (area) corresponds to one pixel or so may be critical, causing a short circuit, an open or the like in interconnection. Alternatively, in a case where a coarse and sparse pattern is formed, a defect of one pixel or so mostly has little effect. In a case where such a dense pattern and a sparse pattern are mixed in a target image, even if the detection sensitivity is changed as appropriate, as shown in Document 1, some small and unnecessary defects are detected to some degree and the efficiency of defect detection is not largely improved, and this requires a long time for an operator or other apparatus to check (review) the picked-up image of the defects.